The X-ray tomosynthesis imaging apparatus disclosed in Japanese Patent Laid-Open No. 57-203430 can reconstruct a plurality of cross sections by acquiring imaged data obtained by one tomosynthesis imaging operation. More specifically, there are disclosed an X-ray generator, a two-dimensional detector, a driving mechanism which moves the X-ray generator and two-dimensional detector in relatively opposite directions, a position detector which detects the movement positions of the generator and detector, a storage device which stores images obtained every relative movement of the above components in association with the respective positions, and a device which computes the storage position of image information at an arbitrary point on a subject to be imaged in the depth direction, and calculates an image display signal.
In CT, in some cases, a scanogram (a projection image which provides an overall view along the body axis direction) which is used to determine a cross section position before imaging of a CT cross section is obtained by imaging in advance, and a cross section position where data acquisition is to be performed is set on the basis of the scanogram. In CT based on the recent spiral scheme, however, a cross section position is not finely set in data acquisition, and a calculated cross section is designated only in calculation of a cross section image.
Note that in this case, the terms “cross section” and “tomosynthesis” are distinctively used. The term “cross section” means a surface like that imaged in CT, which is perpendicular to the body axis of a human body. The term “tomosynthesis” means a surface like that imaged by a conventional analog tomosynthesis imaging apparatus, which is parallel to the body axis of a human body.
Japanese Patent Laid-Open No. 6-217969 discloses a technique of limiting an X-ray irradiation range to only a film surface by controlling an X-ray stop in accordance with a tomosynthesis angle, thereby reducing scattered radiation. This technique is based on consideration of a tomosynthesis angle ξ and a fan angle θ of an X-ray generator in acquiring projection data with respect to a given tomosynthesis surface p in a subject to be imaged in a conventional analog tomosynthesis imaging apparatus.
More specifically, according to this reference, as the tomosynthesis angle ξ increases, the fan angle θ necessary for the formation of the tomosynthesis surface p decreases.
The above tomosynthesis imaging apparatus is used less these days in the clinical field because of CT. However, with advances in digital tomosynthesis imaging techniques, multiple tomosyntheses can be reconstructed by one tomosynthesis imaging operation, thus realizing higher imaging throughput and smaller exposure dose than CT. For such reasons, attention has been given to the tomosynthesis imaging apparatus again.
It is therefore required for a tomosynthesis imaging apparatus as well as a CT to obtain in advance a setting image by imaging, which is used to arbitrarily set a tomosynthesis surface to be tomosynthetically imaged.
More specifically, it is required to improve the efficiency of imaging and subsequent diagnosis by allowing arbitrary setting of the position, range, shape, and the like of a target tomosynthesis surface before tomosynthesis imaging operation, and to reduce the exposure dose of a subject to be examined by irradiating the subject with only radiation necessary for imaging.